The Raman spectroscopic study of supersaturation: ν1 mode of aqueous NH4H2PO4 solution

In this work, it is shown that careful contour analysis of the symmetric stretching mode of H₂PO⁻₄ of ammonium dihydrogen phosphate may reveal certain structural information as the solution varies from the unsaturated state to the supersaturated state. Both the concentration and temperature dependent cases are demonstrated. It is seen that in solutions there can be varying compositions of monomer, dimeric and polymeric aggregates of H₂PO⁻₄ depending on the concentration and temperature. Apparently, there is a thermodynamic point above which the polymeric aggregates cannot be in thermodynamic equilibrium with the monomeric or dimeric species and the solution is therefore thermodynamically unstable. There is also no discontinuity in the half band width and peak frequency as the solution reaches supersaturation consistent with the refractive index and electrical conductivity measurements.     

Characterization of the inclusion complex of β-cyclodextrin with sorbic acid in the solid state and in aqueous solution

Crystal structure of β-cyclodextrin (β-CD) complexes with sorbic acid, usually as food preservative, has been determined by single-crystal X-ray diffraction at 113 K. The space group of β-cyclodextrin-sorbic acid complex is P1 with unit cell dimensions of a = 15.284(3) Å, b = 15.402(3) Å, c = 17.981(4) Å, α = 99.67(3)°, β = 112.83(3)°, γ = 102.48(3)° and Z = 1. The result indicates that the β-CD molecules form head-to-head dimers which pack in the intermediate mode. Each dimer contains two guest molecules whose methyl groups are located at the dimer interface while the carboxyl groups protrude from the β-CD primary faces. Water molecules (25.5) are distributed outside the cyclodextrin cavity over 31 sites. Furthermore, nuclear magnetic resonance spectroscopy (¹H NMR) has been employed to investigate the inclusion behavior between the host β-CD and guest sorbic acid in aqueous solution. The results obtained enabled us to structurally characterize the β-CD inclusion complex with sorbic acid.     

Poly(ethylene oxide) irradiated in the solid state,melt and aqueous solution—a DSC and WAXD study

Interactions of the aggregate state of poly(ethylene oxide), PEO, and γ-irradiation conditions (total dose, atmosphere) on its thermal and crystalline properties were investigated by DSC and WAXD taking into account sample molecular mass and form. In PEO irradiated in the solid state and in the presence of oxygen, chain scission dominated over concurrent crosslinking up to 200 kGy, particularly in PEO powders, due to a large surface being in contact with air. In solid samples the degree of crystallinity and crystallite size increased with the dose up to 50 kGy, probably not just due to partial crystallization upon degradation of amorphous phase, but to recrystallization of broken tie molecules. The least changes in crystallinity and phase transformation temperatures occurred in solid films. A substantial decrease in crystallinity and transformation temperatures without the initial crystallinity increase was achieved in samples that were amorphous on irradiation, at temperatures above the PEO melting temperature and in aqueous solutions. Radiation crosslinking of the PEO aqueous solution in an inert atmosphere is the most suitable way to obtain a lower degree of crystallinity and phase transformation temperatures while preserving mechanical properties.     

The Raman spectra of tetracoordinate CdCl3X2− halogenocadmate(II) anions in the solid state

Anionic halogenocadmate(II) complexes of the type CdCl₃X²⁻ have been prepared and characterized as salts of tetrapropylammonium. The Raman spectra of these crystalline solids have been interpreted in terms of a C_3v symmetry. The tetrachlorocadmate(II) anion also possesses such a symmetry in the solid state.     

Comment on “Vibrational spectra of isomeric pyridinic carboxylic acids in solid state and in solution and their SERS studies in silver soil”

A recent claim that the solid pyridine(mono)carboxylic acids are composed of associated centrosymmetric (RCO₂H)₂ bimolecules is unfounded and incorrect. For solid picolinic acid (a hitherto not wholly solved problem), an ionic structure, NC₅H₄-2-CO⁻₂.2′-HO₂CC₅H₄N⁺H, is put forward here.     

Determination of the protonation state of [H3PW11O39]4− and the stability constant of [Ag(H2O)(H3PW11O39)]3− in aqueous solution

By employing elemental analysis, ³¹P NMR, pH, and conductivity measurements, the protonated state of lacunary heteropolyoxotungstophosphates in aqueous solution, {PW₁₁O₃₉}, is determined to be [H₃PW₁₁O₃₉]^4?. Using it as ligand, a complex of [Ag(H₂O)(H₃PW₁₁O₃₉)]^3? is formed. An electrochemical cell is designed as follows: (?) Hg, Hg₂Cl₂ [Ag(H₂O)(H₃PW₁₁O₃₉)]^3? (aq) | Ag(s) (+) (salt bridge is saturated KNO₃ solution). By measuring the electromotive force of the cell, the stability constant of [Ag(H₂O)(H₃PW₁₁O₃₉)]^3? in aqueous solution is determined to be 4.34 × 10³ (25 °C).     

A study of the thermal analysis of the solid solution (AgxK1−xNO3

The effect of partial replacement of K⁺ by Ag⁺ in the mixed system of KNO₃ and AgNO₃ during a set of DSC heating cycles was studied by means of a modern computerized DSC system. Thermal analysis was performed in the vicinity of the phase transition II I for pure KNO₃. The results revealed a large change in enthalpy and the phase transition temperature close to the morphotropic boundary x=0.5–0.6. At this boundary, the transformation enthalpy reached the maximum value of 101 J g^–1. On the basis of the data obtained from this accurate thermal analysis work, a model is suggested for the energy barrier of rotation of the nitrate ion in the mixed nitrate system.     

Inclusion of Paracetamol into β-cyclodextrin nanocavities in solution and in the solid state

We report on steady-state UV-visible absorption and emission characteristics of Paracetamol, drug used as antipyretic agent, in water and within cyclodextrins (CDs): β-CD, 2-hydroxypropyl-β-CD (HP-β-CD) and 2,6-dimethyl-β-CD (Me-β-CD). The results reveal that Paracetamol forms a 1:1 inclusion complex with CD. Upon encapsulation, the emission intensity enhances, indicating a confinement effect of the nanocages on the photophysical behavior of the drug. Due to its methyl groups, the Me-β-CD shows the largest effect for the drug. The observed binding constant showing the following trend: Me-β-CD>HP-β-CD>β-CD. The less complexing effectiveness of HP-β-CD is due to the steric effect of the hydroxypropyl-substituents, which can hamper the inclusion of the guest molecules. The solid state inclusion complex was prepared by co-precipitation method and its characterization was investigated by Fourier transform infrared spectroscopy, 1H NMR and X-ray diffractometry. These approaches indicated that Paracetamol was able to form an inclusion complex with CDs, and the inclusion compounds exhibited different spectroscopic features and properties from Paracetamol.     

The interaction of biliar acids with 2-hydroxypropyl-β-cyclodextrin in solution and in the solid state

The interaction of two biliar acids (chenodeoxycholic acid and cholic acid) with 2-hydroxypropyl--cyclodextrin (HPCD) in solution and in the solid state was studied using different techniques. The formation of an inclusion complex with a 1:1 stoichiometry was suggested by the phase solubility studies. Both differential scanning calorimetry and X-ray diffractometry exhibited the amorphous state of the complex. The inclusion of both biliar acids into the HPCD cavity was confirmed by the¹³C-NMR studies. Cholic acid showed a weaker affinity with respect to chenodeoxycholic acid probably owing to the presence of a hydroxyl group onC(12) (12) close to the complexation site.     

Inclusion complexes of Sulconazole with β-cyclodextrin and hydroxypropyl β-cyclodextrin: characterization in aqueous solution and in solid state

Complexation between sulconazole (SULC), an imidazole derivative with in vitro antifungal and antiyeast activity, and β-cyclodextrins (β-CD and HP-β-CD) was studied in solution and in solid states. Complexation in solution was evaluated using solubility studies and nuclear magnetic resonance spectroscopy (¹H-NMR). In the solid state, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and RX diffraction studies were used. Solubility studies suggested the existence of inclusion complex between SULC and β-CD or HP-β-CD. ¹H-NMR spectroscopy studies showed that the complex formed occurs by complexation of imidazole ring into inner cavity. DSC studies showed the existence of a complex of SULC with β-CD. The TGA and RX studies confirmed the DSC results of the complex. Solubility of SULC in solid complexes was studied by the dissolution method and it was found to be much more soluble than the uncomplexed drug.     

Valence state of cobalt atoms and crystal structure of YBa2Cu3−x-CoxO6+δ solid solution

The crystal structure of YBa₂Cu_3−xCo_xO_6+δ solid solutions, where x = 0.2, 0.4, 0.6, and 0.8, was studied by powder neutron diffraction. The charged states of the cations were calculated using the interatomic distances obtained in neutron diffraction measurements. It is shown that cobalt in the Cul position has valence 3+ and octahedral environment for x = 0.2 and 0.4. As x increases, the valence of some cobalt ions in the above positions changes to 4+, the environment changes to tetrahedral, and copper in the Cu2 position is partly substituted. Cobalt in the Cu2 positions has valence 2+ and does not change the square pyramidal arrangement of oxygen ions surrounding this position. Translated fromZhurnal Strukturnoi Khimii, Vol. 41, No. 4, pp. 765-771, July-August, 2000 This work was supported by the “Advanced Research in Physics of Condensed State” Program ( “Superconductivity” project 96-051 and “Neutron Studies of Condensed Media” project 4), Leading Scientific Schools of Russian Federation State Support Program grant No. 96-15-96515, and RFFR grant No. 98-03-32510a.     

Interaction of naproxen with α-, β-, and γ-hydroxypropyl cyclodextrins in solution and in the solid state

Solid combinations of naproxen with amorphous hydroxypropyl derivatives of -, -, and -cyclodextrin with an average substitution degree per anhydroglucose unit of 0.6 were investigated for thermal behaviour (differential scanning calorimetry), drug crystallinity (X-ray diffractometry), and dissolution rate (dispersed amount and rotating disc methods). Phase-solubility analysis and computer-aided molecular modelling were carried out to study the inclusion complexation of naproxen with hydroxypropyl cyclodextrins. The cavity size of the host is a selective factor for the solubilizing effect, complexing ability, and dissolution rate enhancement on naproxen, hydroxypropyl -cyclodextrin being markedly the most effective derivative. No relationship was found between the decrease in crystallinity of the drug dispersed in the amorphous carrier matrix and the geometrical features of the cyclodextrin macrocycle.     

Sodium motion in the Nasicon related Na1+xZr2−xInx(PO4)3 solid solution: An NMR study

Sodium ion motion in Na_1+xZr_2−xIn_x(PO₄)₃ Nasicon-related materials (0 ≤ x ≤ 1.85) has been studied by NMR at two resonance frequencies from 170 to 450 K. At 8 MHz the resonance lines due to M1- and M2-type sites are well resolved. They are split by a strong second-order quadrupolar effect (ν_Q = 1.5 Megacycles (Mc)/sec). For NaZr₂(PO₄)₃ only the M1 site is occupied at RT, while a new site M5 appears at rising temperature (410 K). At 21 Mc/sec the line narrowing observed at increasing temperature illustrates the Na⁺ ion mobility within the skeleton. According to the temperature and the value of the ionic conductivity two diffusion mechanisms seem to occur.     

Inclusion complexes of 5-flucytosine with β-cyclodextrin and hydroxypropyl-β-cyclodextrin: characterization in aqueous solution and in solid state

Complexation between 5-flucytosine (5-FC), a cytosine analogue with in vitro antifungal and antiyeast activity, and β-cyclodextrins (β-cyclodextrin and hydroxypropyl-β-cyclodextrin) was studied in solution and in solid states. Complexation in solution was evaluated using solubility studies, UV–vis and ¹H-NMR. In the solid state, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), FT-IR and X-ray diffraction studies were used. UV–vis, FT-IR and ¹H-NMR spectroscopy studies showed that the complex formed occurs by complexation of piridinique base analogue into inner cavity. DSC studies showed the existence of a complex of 5-FC with β-CDs. X-ray studies confirmed the DSC results of the complex existence. Solubility studies showed that the complexed drug is forty times more soluble than free 5-FC, indicating the obtained systems as future, promising drug carriers.     

Modes of coordination and stereochemistry of the NO3 − anions in inorganic nitrates

Stereochemical features of 950 nitrate groups in the structures of 365 inorganic nitrates were analyzed using TOPOS software. The types of coordination of nitrate groups are systematized by means of Voronoi-Dirichlet polyhedra and the method of intersecting spheres. Terminal coordination (53% of the total number of nitrate groups), most of all terminal bidentate coordination (47%) was found to prevail. Bridging nitrate groups occur less frequently (20%). A considerable number of nitrate groups are not incorporated in the coordination sphere of the complexing atom but form H-bonds or bonds of mainly ionic nature (27%). A number of metal cations show clear-cut tendency for a certain mode of coordination of the NO₃ group. Criteria for classification of nitrate groups into four types (slightly distorted groups and groups with monodentate, bidentate and asymmetric type distortion) are proposed. Structural features of nitrate groups depending on the mode of coordination are considered. The geometry of mono- or bidentate nitrate groups can differ appreciably from the typical one because of participation of terminal oxygen atoms in ionic or hydrogen bonds. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 429–440, March, 2008.